Commercial methods for producing dicarboxylic acids generally involve oxidizing naphthenes, cycloaliphatic ketones or cycloaliphatic alcohols with nitric acid in the presence of metal oxidation catalysts.
In the case of adipic acid, specific feed materials such as cyclohexane, cyclohexanone and/or cyclohexanol in admixture with nitric acid are heated at about 40.degree.-140.degree. C. in the presence of a catalyst. The resultant oxidation reaction product comprises adipic acid together with small amounts of monocarboxylic acids and dicarboxylic acids and other organic components in admixture with nitric acid and catalyst components. A substantial quantity of the adipic acid product is recovered by cooling the solution and filtering off the crystallized adipic acid. Oxidation methods of adipic acid production are described in U.S. Pat. Nos. 2,439,513; 2,557,281; 2,719,566; 2,840,607; 2,971,010; 3,338,959; and references cited therein.
In a process involving nitric acid oxidation of cyclohexanone and/or cyclohexanol, economically significant amounts of succinic acid and glutaric acid are formed as byproducts in admixture with the adipic acid. After the major portion of the adipic acid is separated by crystallization and filtration, the aqueous filtrate mother liquor contains some adipic acid, as well as succinic acid, glutaric acid, nitric acid and metal catalyst values.
Usually this filtrate has been treated as a waste stream. Because of environmental and economic considerations, there has been continuing research effort to develop methods for recovering the valuable and reusable organic and inorganic components of the said waste filtrate byproduct stream.
U.S. Pat. No. 3,726,888 describes a process for the separation and recovery of the components contained in the filtrate byproduct stream of an adipic acid manufacturing plant. The filtrate stream comprises an aqueous solution of adipic acid, glutaric acid, succinic acid, metal catalyst values and nitric acid. The separation and recovery process involves contacting the filtrate with alkanol, and extracting with a water-immiscible organic solvent to provide an organic phase containing the formed esters, and to provide an aqueous phase containing the nitric acid and metal catalyst values. Each of the phases is fractionated to separate the mixtures into useful components.
U.S. Pat. Nos. 4,076,948 and 4,082,788 describe processing improvement which are adapted to overcome some of the difficulties characteristic of the byproduct separation and recovery technology disclosed in the above recited U.S. Pat. No. 3,726,888.
Among the problems encountered during the handling and treatment of the described filtrate byproduct stream from adipic acid manufacture is the fact that the said filtrate byproduct stream contains a relatively high water content. If the filtrate byproduct stream is concentrated by vacuum distillation to reduce the water content, the resultant concentrate solution solidifies at ambient temperatures. Consequently, it is then necessary to maintain the temperature of the concentrate solution at a temperature above about 75.degree. C. during storage or shipping in order to prevent the concentrated solution from solidifying. For example, large volume shipments require the use of tankcars equipped with heating coils.
There remains a need for improvements in the technology relating to the handling and treatment of a dilute aqueous filtrate byproduct stream which is a waste effluent from an adipic acid manufacturing plant.
Accordingly, it is an object of this invention to provide a method for improving the economics of handling and treating a waste effluent from an adipic acid manufacturing plant.
It is another object of this invention to provide a process for converting a dilute aqueous filtrate byproduct stream from adipic acid manufacture into a concentrate solution which does not solidify at ambient temperatures.
It is a further object of this invention to provide an improved process for the separation and recovery of dicarboxylic acids and other valuable components contained in a filtrate byproduct stream derived from an adipic acid manufacturing operation, which operation involves nitric acid oxidation of cyclohexanone and/or cyclohexanol.
Other objects and advantages of the present invention shall become apparent from the accompanying description and Example.